CORE LAB: PROPERTIES OF IONIC AND MOLECULAR COMPOUNDS
Core Lab: Properties of Ionic and Molecular Compounds
Unit 3: Chemical Reactions
Teacher Notes:
•
The main purpose of this lab is for the students to determine the differences between ionic and
molecular compounds.
•
The key is to select compounds that will be a representative sample, to illustrate the desired
properties (Some compounds are listed but many may be substituted). To help define
operationally, students should be able to complete the following table*.
Generalizations:
Classification of
substances
phase at room
temp
solubility in
water
color of solution
(if applicable)
conductivity of
solution
ionic
solid
yes, to varying
degrees
colored or
colorless
yes, to varying
degrees
molecular
solid, liquid or
gas
yes or no
colorless
no
* sample responses are in italics.
•
When attempting to dissolve solids in water be sure to use a small amount of solid. If a large
amount is used, often times some of it will dissolve but the student will interpret the result as if
it wasn’t soluble, because they still see the solid in the water.
•
It may be practical to set this activity up in stations (each having one or two substances) and get
the students to rotate from station to station
•
If student use of the conductivity apparatus is not feasible at each station, the teacher may go
around and test each station as the activity proceeds and share the results with the class.
•
At the conclusion of the lab it should be pointed out that acids do not have the physical
characteristics of either ionic or molecular compounds. Acids may be solid, liquid, or gas;
dissolve in water to varying degrees; form colorless solutions; and form conducting solutions (to
varying degrees).
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SCIENCE 1206 CURRICULUM GUIDE
CORE LAB: PROPERTIES OF IONIC AND MOLECULAR COMPOUNDS
Compounds can often be categorized based on the properties they possess. In this activity you will be
given a number of compounds which you will first categorize as ionic or molecular based on their
chemical formula. You will then determine a number of properties of these compounds and on that
basis make generalizations for distinguishing between ionic and molecular substances.
Problem:
Given a number of compounds, make observations and carry out tests to distinguish
between ionic and molecular compounds
Materials:
Samples of the following compounds in labeled covered containers (these are only
suggestions):
ammonium chloride
ethanol
methanol
potassium chloride
n-pentane
zinc sulfate
copper(II) sulfate
potassium chromate
sucrose
potassium iodide
mineral oil
sodium phosphate
propane
sodium hydroxide
sodium chloride
potassium permanganate
Procedure: 1. Add 25 mL of deionized water to a 50 mL beaker
2. Add a small quantity (size of a pea) of the substance to the water (if it is a gas
simply allow some to bubble through the water)
3. Use a stirring rod to stir the water and substance added
4. Record in the data table the following:
(i) phase at room temperature
(ii) whether or not you believe the substance dissolved in water (soluble)
(iii)color of solution (if substance was soluble). Note: clear is not a color (all
solutions are clear), use the term colorless if there is no color
(iv) conductivity of solution (if substance was soluble). Note: You should
compare the conductivity of the solution to that of the deionized water (this
is the control)
5. Pour the water off any substance that did not dissolve and add the undissolved
substance to the waste beaker provided
6. Pour any solutions down the sink.
7. Rinse the beaker and test the next substance
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CORE LAB: PROPERTIES OF IONIC AND MOLECULAR COMPOUNDS
Results:
Table 1
Prelab Exercise
Name of substance
formula
ionic or
molecular
phase at
room temp.
(s, l, or g)
soluble in
water
(yes/no)
color of
solution
conductivity
of solution
1.
2.
3.
4..
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
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SCIENCE 1206 CURRICULUM GUIDE
CORE LAB: PROPERTIES OF IONIC AND MOLECULAR COMPOUNDS
Table 2
Generalizations
Classification of
substances
phase at room
temp
solubility in
water
color of
solution
conductivity of
solution
ionic
molecular
Questions: 1. Electrical conductivity was used in this activity to test solutions of various
compounds. Why should the electrical conductivity of deionized water be tested
before testing the conductivity of the solution?
2. Can a substance be classified as ionic or molecular based on its phase at room
temperature? Explain.
3. Can a substance be classified as ionic or molecular based on whether it dissolves in
water? Explain
4. Can a substance be classified as ionic or molecular based on the color of its solution
(assuming it dissolves in water)? Explain.
5. Can a substance be classified as ionic or molecular on the basis of the electrical
conductivity of its solution (assuming it dissolves in water)? Explain.
6. Complete the following table:
Table 3
properties of the pure substance
ionic, molecular, or ?
a solid which dissolves in water to form a colorless, nonconducting
solution
a liquid which dissolves in water to form a colorless solution
a solid which dissolves in water to form a colorless solution
a solid which dissolves in water to form a colored solution
a solid which does not dissolve in water
a gas at room temperature
a substance which forms a conducting solution
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